linux-kernel - Re: [PATCH v10 2/3] Documentation: driver-api: pps: Add Intel Timed I/O PPS generator

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Message-ID: <2024061215-deflected-dimness-a317@gregkh>
Date: Wed, 12 Jun 2024 10:03:22 +0200
From: Greg KH <gregkh@...uxfoundation.org>
To: lakshmi.sowjanya.d@...el.com
Cc: tglx@...utronix.de, giometti@...eenne.com, corbet@....net,
	linux-kernel@...r.kernel.org, linux-doc@...r.kernel.org,
	andriy.shevchenko@...ux.intel.com, eddie.dong@...el.com,
	christopher.s.hall@...el.com, pandith.n@...el.com,
	subramanian.mohan@...el.com, thejesh.reddy.t.r@...el.com
Subject: Re: [PATCH v10 2/3] Documentation: driver-api: pps: Add Intel Timed
 I/O PPS generator

On Wed, Jun 12, 2024 at 10:02:46AM +0200, Greg KH wrote:
> On Wed, Jun 12, 2024 at 09:23:58AM +0530, lakshmi.sowjanya.d@...el.com wrote:
> > From: Lakshmi Sowjanya D <lakshmi.sowjanya.d@...el.com>
> > 
> > Add Intel Timed I/O PPS usage instructions.
> > 
> > Co-developed-by: Pandith N <pandith.n@...el.com>
> > Signed-off-by: Pandith N <pandith.n@...el.com>
> > Signed-off-by: Lakshmi Sowjanya D <lakshmi.sowjanya.d@...el.com>
> > Reviewed-by: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
> > Acked-by: Rodolfo Giometti <giometti@...eenne.com>
> > ---
> >  Documentation/driver-api/pps.rst | 24 ++++++++++++++++++++++++
> >  1 file changed, 24 insertions(+)
> > 
> > diff --git a/Documentation/driver-api/pps.rst b/Documentation/driver-api/pps.rst
> > index 78dded03e5d8..75f7b094f963 100644
> > --- a/Documentation/driver-api/pps.rst
> > +++ b/Documentation/driver-api/pps.rst
> > @@ -246,3 +246,27 @@ delay between assert and clear edge as small as possible to reduce system
> >  latencies. But if it is too small slave won't be able to capture clear edge
> >  transition. The default of 30us should be good enough in most situations.
> >  The delay can be selected using 'delay' pps_gen_parport module parameter.
> > +
> > +
> > +Intel Timed I/O PPS signal generator
> > +------------------------------------
> > +
> > +Intel Timed I/O is a high precision device, present on 2019 and newer Intel
> > +CPUs, that can generate PPS signals.
> > +
> > +Timed I/O and system time are both driven by same hardware clock. The signal
> > +is generated with a precision of ~20 nanoseconds. The generated PPS signal
> > +is used to synchronize an external device with system clock. For example,
> > +it can be used to share your clock with a device that receives PPS signal,
> > +generated by Timed I/O device. There are dedicated Timed I/O pins to deliver
> > +the PPS signal to an external device.
> > +
> > +Usage of Intel Timed I/O as PPS generator:
> > +
> > +Start generating PPS signal::
> > +
> > +        $echo 1 > /sys/devices/platform/INTCxxxx\:00/enable
> > +
> > +Stop generating PPS signal::
> > +
> > +        $echo 0 > /sys/devices/platform/INTCxxxx\:00/enable
> 
> Why is this not described in Documenation/ABI/ ?

Oops, that was patch 3/3, sorry.